It is well known that heavy metals can be detrimental to human health even at low concentrations. Traditionally, effects of heavy metals have been assayed singly, monitoring the effects of a particular metal or a suite of individual metals on model organisms. Rotifers have been used as model organisms for toxicity testing of water supplies because of their short life spans, high reproductive outputs, and ease of manipulation. These features make them ideal for rapid toxicological assessment. During the last 10 years, there has been a great deal of interest in the use of sublethal indicators of exposure and effects of environmental contaminants on health. One of the newest biomarkers being explored by environmental scientists is the use of genetic diversity to assess ecological health. Genetic diversity within a species normally is quite varied. This diversity is the basis for a large gene pool that allows populations of organisms to persist in the face of environmental change. The genetic integrity of populations is critical to their long-term survival. Recent studies have shown that genetic diversity is compromised in contaminated environments. The lack of species diversity in degraded environments has been documented for many years, but genetic diversity within a species also appears to be reduced. The goals of the proposed research are to determine whether exposure to heavy metals (Arsenic, copper and lead) can impact the genetic structure of a population over 20 generations, and how exposure impacts organisms' responses to secondary exposures. A model organism, the rotifer Plationus patulus, will be subjected to metal exposures over 20 generations. Genetic variation will be monitored in the initial population, at generations 5, 10 and 20. Amplified fragment length polymorphism will be used as the biomarker of genetic variation. This is a DNA fingerprinting technique that allows the calculation of genetic variation and a number of other population genetic statistics. Concentrations of all metals will be at environmentally relevant levels. Following metal exposure, animals will be monitored for response to low pH, low food levels and a pesticide. Results obtained using organisms with rapid generational turnover times, such as rotifers, may give us some idea of what to expect when longer- lived species, including humans, are exposed to toxicants over generations.